It's important to criticize venture capital for the right reasons. VCs correctly care about value, not revenue or profit, but by itself this isn't a problem because the few most valuable companies typically dominate the returns, and they are virtually always insanely profitable in the long run. VCs thus don't deserve derision for not caring about revenue or profit in the short term.
On the other hand, because only the top few companies matter to a VC's returns, the VC's incentives are not always well-aligned with the interests of the founders. This is because VCs can invest in a large number of companies and thus realize the expected value of their investments (due to the law of large numbers [2]). Founders, on the other hand, even if they are insanely prolific, can probably only start a handful of companies in a lifetime, and are thus exposed to a much higher variance in outcomes.
For example, if the founders have a choice between a 50% chance of making a $50m company (expected value $25m) and a 1% chance of making a $10b company (expected value $100m), VCs have a strong incentive to push for the latter, even though most founders would prefer the former. This mismatch of incentives, not a lack of focus on revenue or profit, is the real problem with VC (at least from a founder's point of view).
VCs actually have a solution to this incentive mismatch: when you ask a not-yet-wealthy founder to swing for the fences (which typically happens during an investment round) you invite them to take some of the investment money out of the company and into their personal accounts.
How could YC possibly keep statistics on revenue for the entire portfolio?
Sam isn't saying "we don't care about revenue", he's saying "we don't have any way to keep statistics on the total revenue of all portfolio companies". Those are very very different statements.
Ahhh, yet another reminder as to what matters and what doesn't in the game of VC.